Various types of positioning systems which employ alternating electromagnetic fields are known. The following U.S. Patents and foreign patent documents are believed to represent the state of the art:
U.S. Pat. Nos. 4,054,881 and 4,314,251 to Raab; 4,622,644 to Hansen; 4,737,794 to Jones; 4,613,866, 4,945,305 and 4,849,692 to Blood, 4,017,858 and 4,298,874 and 4,742,356 to Kuipers; 5,168,222 to Volsin et al; 5,0170,172 to Weinstein; and 5,453,686 to Anderson; WO 94/04938 to Bladen.
U.S. Pat. No. 4,710,708 to Rorden describes a positioning system which employs only one magnetic coil.
Genetic algorithms are described in Genetic algorithms in search: optimization and machine learning, D. Goldberg, 1989; and
An introduction to genetic algorithms, Melanie Mitchell, 1996.
PLL technology is described in Phase locked loop: simulation and applications, by Roland E. Best, McGraw-Hill Book Company, ISBN 0070060517.
The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference.